This invention relates to a hitch adapter for connecting a tractor drawbar to the tongue of a trailing implement for the purpose of locating the articulation axis between the tractor and the implement equidistantly between the front and rear universal joints of the power take-off shaft assembly that connects the tractor power take-off to the implement drive shaft.
The use of such hitch adapters results in equal angles of articulation of the front and rear joints and thereby eliminates speed variations and vibrations in the implement drive train which would exist if the angles were not equal. Hitch adapters are described in various patents, such as U.S. Pat. Nos. 3,557,892, 4,008,905, and 4,156,473. These exemplify various types of quick-attach designs which, in an attempt to accommodate the wide varieties of drawbar shapes and thickness available in agricultural tractors while maintaining a snug fit, tend to produce complex, heavy, and expensive structures.
Less of a problem than drawbar shape are the drawbar holes which are somewhat standardized in Society of Automobile Engineers Standard No. SAE J1170 (A.S.A.E. S338).
The simplest and lowest cost hitch adapter design is a bolt-on extension bar which moves the main hitch point between the implement and tractor rearward. However, the major obstacle to this type of design is that installation and removal is more time consuming than a quick-attach design and requires the use of multiple wrenches to achieve satisfactory rigidity between the hitch adapter and the tractor drawbar.